And even Miss Dinsey, who is best
known for posting photographs of herself in revealing outfits on her
blog, said she was surprised by the decision, saying she believed she
was chosen because she ticked the ‘young, female box’.

Mr Murphy said Newsnight researchers
contacted him while preparing Thursday’s programme, on corporation tax,
because they wanted to use some of his extensive studies on tax
avoidance by major companies.

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But when he offered to appear on the
panel he was told it would not be possible because it would ‘upset the
gender balance’.

Instead, he had to sit at home and watch Miss O’Hagan
talk about his own research.

To make matters worse, alongside her was Miss Dinsey, an economics graduate and founder of the ‘What I Wore Today’ website.

It features daily shots of her in outfits including plunging tops, bikinis, and, once, a Playboy bunny costume.

Before Thursday’s show, she tweeted
that she was heading to the studio straight from a waxing salon, joking
that she was going from ‘waxes to taxes ... I feel very Legally Blonde.’

She added: ‘Whenever I don’t know the answer I’ll just refer people to my amazing “specially threaded for Newsnight” brows.’

In the event Miss Dinsey appeared a little nervous on air, giving composed if slightly rambling answers when asked by presenter Gavin Esler whether it was wrong for major firms to pay comparatively small amounts of tax.

Snubbed: Richard Murphy says he was discriminated against for being a man

The two women were joined by Bill Dodwell, head of tax policy at accountancy firm Deloitte. Before the debate, Mr Esler interviewed Treasury minister David Gauke.

According to Mr Murphy, the show’s researchers told him he couldn’t appear because Mr Dodwell had been chosen to put the multinationals’ view and, due to the BBC’s strict ‘gender balance’ rules, they needed a woman – Miss O’Hagan – to put the opposing argument.

Mr Murphy said: ‘It’s an utterly absurd situation where Newsnight will overlook a story about paedophilia but obsess about gender balance rules.

‘They were so desperate to have a woman they took someone less expert over someone more expert, and the person who had done the investigation and developed the techniques was deliberately not allowed on air. This is straightforward discrimination.’

‘We are a tiny campaign. I do all the work – there’s no credible alternative to talk about this kind of investigation.

‘Ellie Mae O’Hagan did quite a good job but she’s not an accountant. She just talked about my work.’ Miss Dinsey, a graduate of University College London, said she was also surprised by the decision not to invite Mr Murphy on the programme and said she had not been told about the selection criteria.

She added: ‘If he was willing to be on it and wasn’t invited it was a bit mean. I was having a bit of a laugh with my friends about being on it.

‘There are certainly opportunities that I get for being a young businesswoman that young businessmen don’t get.

‘I believe you should get the best person for the job, whoever that is. On a programme like Newsnight it should be the best person to speak on the subject.’

A BBC spokesman said: ‘Newsnight aims to have a varying range of voices. We contacted Mr Murphy to see if he could recommend other experts in this field to broaden the discussion.

‘We are sorry if he was disappointed not to have been asked to appear in this particular programme.’

The show focused on how the 19 biggest firms in Britain were paying as little as 3 per cent tax.

Experts estimate the Exchequer is missing out on £3.3billion in potential revenue.